FORMATION OF GALLS 199 



development of the gall can be brought to a stop by the death of the 

 larva. We know that wound-stimulus does not play the chief part in 

 the formation of galls, because in many cases the eggs are fixed on the 

 surface of young organs of plants, and are then invested from the sides 

 by the tissue which lies round about them. The larval chamber, which is 

 always lined with nutritive tissue for the larva, arises through an arrest 

 of growth at the position of the young gall-tissue which is immediately 

 in contact with the larva. 



Adler discovered, and Beyerinck has confirmed his statement, that 

 the different forms of one and the same gall-wasp produce different' 

 forms of galls upon one and the same host-plant the oak ; and this is of 

 special importance in relation to any theory of the formation of galls. The 

 females of Dryophanta folii, for example, leave their galls upon the oak- 

 leaves in November or December ; they seek out a bud, a ' sleeping eye,' 

 lay an egg upon its vegetative point, and thereby produce a small violet- 

 coloured bud-gall which, before its true connexion was discovered, was 

 ascribed to a gall-wasp termed Spathegaster Taschenbergi. The males 

 and females of this species leave their habitations in May, the fertile 

 females prick the ribs of young oak-leaves and thereby occasion the 

 formation of the leaf-galls from which we started. The two kinds of 

 galls are quite different both in form and anatomical structure. The 

 question then is is the material, causing the formation of the gall, which 

 is excreted from the eggs originating parthenogenetically, different from 

 that exuding from the fertilized eggs, or, if the material be the same, is 

 its reaction on a vegetative point different from that which it exerts 

 upon a leaf? The answer to this question I consider of more importance 

 for morphology than the pursuit after apical cells and other questions of 

 detail upon which so much time has been expended. 



The galls are adapted in a remarkable degree to the needs of the 

 larvae, as has been already stated, and it is of special interest to observe 

 that the protection of the developing insect in the gall is effected partly 

 mechanically, partly chemically especially by a copious formation of 

 tannin but the protection is in no degree absolute, as the numerous 

 inhabitants of the galls tell. 



How remarkable are the formations which arise in this way is 

 shown in the galls of the microlepidopterous Cecidotes Eremita which 

 are found on the twigs of shrubs of the genus Duvaua 1 in Argentina. 

 The spherical to oval gall arises from the cambium of the branch ; it 

 possesses a cambial meristem lying parallel with its surface from which 

 is 'developed in a radial direction inwards a nourishing tissue of thin- 

 walled cells rich in protoplasm for the caterpillar, whilst towards the outside 



1 Hieronymus, in Jahresber. der Schlesischen Gesellschaft fur Vaterland-Cultur, 1884, p. 272. 



